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ABSTRACT Spider pulsars are compact binary systems composed of a millisecond pulsar and a low-mass companion. Their X-ray emission – modulated on the orbital period – is interpreted as synchrotron radiation from high-energy electrons accelerated at the intrabinary shock. We perform global two-dimensional particle-in-cell simulations of the intrabinary shock, assuming that the shock wraps around the companion star. When the pulsar spin axis is nearly aligned with the orbital angular momentum, we find that the magnetic energy of the relativistic pulsar wind – composed of magnetic stripes of alternating field polarity – efficiently converts to particle energy at the intrabinary shock, via shock-driven reconnection. The highest energy particles accelerated by reconnection can stream ahead of the shock and be further accelerated by the upstream motional electric field. In the downstream, further energization is governed by stochastic interactions with the plasmoids/magnetic islands generated by reconnection. We also extend our earlier work by performing simulations that have a larger (and more realistic) companion size and a more strongly magnetized pulsar wind. We confirm that our first-principles synchrotron spectra and light curves are in good agreement with X-ray observations.
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Global Kinetic Modeling of the Intrabinary Shock in Spider Pulsars
Abstract Spider pulsars are compact binary systems composed of a millisecond pulsar and a low-mass companion. The relativistic magnetically dominated pulsar wind impacts onto the companion, ablating it and slowly consuming its atmosphere. The interaction forms an intrabinary shock, a proposed site of particle acceleration. We perform global fully kinetic particle-in-cell simulations of the intrabinary shock, assuming that the pulsar wind consists of plane-parallel stripes of alternating polarity and that the shock wraps around the companion. We find that particles are efficiently accelerated via shock-driven reconnection. We extract first-principles synchrotron spectra and light curves, which are in good agreement with X-ray observations: (1) the synchrotron spectrum is nearly flat,Fν∝ const; (2) when the pulsar spin axis is nearly aligned with the orbital angular momentum, the light curve displays two peaks, just before and after the pulsar eclipse (pulsar superior conjunction), separated in phase by ∼0.8 rad; (3) the peak flux exceeds the one at the inferior conjunction by a factor of 10.
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- Award ID(s):
- 1903412
- PAR ID:
- 10368899
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 933
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 140
- Size(s):
- Article No. 140
- Sponsoring Org:
- National Science Foundation
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